Scanning transmission electron microscopy (STEM) with aberration correction is a powerful imaging method to resolve real-space local crystallography on the atomic scale with the high precision. Combining this imaging tool with electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX), this approach revealed that the cation disorder phenomenon mainly occurs on the surface of the NCM materials (usually less than 10-nm deep to the surface) and the interlayer mixing between transition metals and Li and the related local structure changes is strongly dependent on the type of transition metals.1-3

In this work, the cation-disordered layer of the LiNi_0.5Co_0.2Mn_0.3O₂ cathode materials for Li ion battery is controlled by adjusting the ratio of lithium to transition metal, which has been found to have a definite relationship with battery performance. In addition to image analysis using STEM, atomic distribution analysis using EDS and distribution of the oxidation state by EELS were performed. In order to elucidate the origin of this effect from the view point of atomic structure. In particular, the structural characteristics were established through STEM image simulation software based on STEM results. The effect of the structure on the electronic conductivity was investigated by chemical calculation. In addition to the chemical calculated results, the physical phenomenon was observed through the current atomic force microscopy (C-AFM) experiment in the controlled region which is grainboundary in this study, and it was found that the electrochemical performance of the Li ion battery is improved due to the high electronic conductivity in the grain-boundary.

[1] Yan, P.; Zheng, J.; Lv, D.; Wei, Y.; Zheng, J.; Wang, Z.; Kuppan, S.; Yu, J.; Luo, L.; Edwards, D.; Olszta, M.; Amine, K.; Liu, J.; Xiao, J.; Pan, F.; Chen, G.; Zhang, J.-G.; Wang, C.-M. Chemistry of Materials 2015, 27, (15), 5393-5401.

[2] Xiong, X.; Wang, Z.; Yue, P.; Guo, H.; Wu, F.; Wang, J.; Li, X. Journal of Power Sources 2013, 222, 318-325.

[3] Chen, Z.; Wang, J.; Chao, D.; Baikie, T.; Bai, L.; Chen, S.; Zhao, Y.; Sum, T. C.; Lin, J.; Shen, Z. 2016, 6, 25771.